iSCSI SANs inch closer to reality

Posted on January 01, 2002

End users are aware of the potential benefits of building storage networks based on the emerging iSCSI protocol, which enables block-level storage traffic over standard IP networks (IP SANs), but a number of gating factors have delayed adoption. One of the biggest has been a lack of iSCSI host I/O cards with TCP/IP offload engines (TOEs), which are necessary to achieve the performance required by most storage applications.

Alacritech recently became the first to ship a board that accelerates both standard Ethernet network traffic and IP storage (iSCSI) traffic. The card offloads TCP/IP and iSCSI protocol processing from the host CPU and software to a custom onboard ASIC.

Larry BoucherAlacritech

Click here to enlarge image

"This is the first shipping product that runs iSCSI at wire speed [1Gbps in the case of Gigabit Ethernet]," claims Larry Boucher, founder, chairman, president, and CEO of Alacritech. (He also founded Adaptec and network-attached storage [NAS] pioneer Auspex Systems.) Analysts agree that Alacritech may have first-to-market bragging rights, but they say that advantage may be short-lived and that, even with the advent of iSCSI server cards, end-user adoption of IP SANs will still be slow (see chart on p. 15).

A number of network interface card (NIC) and host bus adapter (HBA) vendors, including Adaptec, Agilent, Emulex, Intel, QLogic, and others, are expected to ship competing boards in the first half of the year (see "iSCSI adapter vendors jockeying for position," below).

For now, Alacritech is just shipping its "1000x1 Server and Storage Accelerator" to OEMs, and qualification cycles can take months to a year before OEMs begin shipments to users. The company plans to begin shipping direct to users within the next quarter, according to Boucher. Alacritech refers to the iSCSI/TOE card as an Integrated Storage Network Interface Card, a term adopted by some storage analysts (see "Networking and storage converge on IS-NICs," right).

The industry has not settled on standard terminology for emerging iSCSI server cards, but it is likely that vendors with strong networking backgrounds will refer to the host cards as NICs, while vendors coming primarily from the storage side will refer to them as HBAs. That dividing line may also include significant price/performance differences.

Despite the availability of iSCSI TOE cards in the first half of this year, there are still a number of gating factors that may stall end-user adoption of IP SANs:

The iSCSI standard is not finalized. Most participants predict that the spec will be ratified by the Internet Engineering Task Force (IETF) in the second quarter. At least for large IT organizations, a completed standard is a requisite for adoption.

Although iSCSI host adapters round out the server side of the IP SAN picture, building an end-to-end iSCSI SAN will require iSCSI target devices such as disk arrays and tape libraries. Several tape library manufacturers recently announced plans to support iSCSI (see "Tape library vendors embrace iSCSI," p. 14), but it may be some time before disk array vendors are on board.

So far, IBM is the only large vendor with an iSCSI disk array (the 200i), although a few smaller array vendors such as 3ware are also shipping "pre-iSCSI" arrays. But even IBM officials admit that the performance of the 200i is not up to the requirements of gigabit-speed configurations. Most analysts predict that high-performance iSCSI arrays from multiple RAID vendors won't be available until at least the second half of this year.

Another gating factor to end-user adoption of iSCSI SANs is a lack of management tools from software vendors.

The final hurdle is interoperability between iSCSI products from different vendors, which is still unproven despite a number of interoperability "plugfests." Lack of interoperability was one of the major roadblocks to adoption of Fibre Channel SANs, although iSCSI interoperability is expected to proceed more quickly and smoothly because it is based on the well-established TCP/IP standard. Also making interoperability easier (than with Fibre Channel), end users can build iSCSI SANs using standard, low-cost Ethernet switches.

Alacritech's NIC

Alacritech has been shipping 100Mbps Ethernet accelerator cards for more than a year, but its "1000x1 Server and Storage Accelerator" is the first to add support for iSCSI and Gigabit Ethernet. The card is based on the company's proprietary Session Layer Interface Card (SLIC) technology and a custom ASIC that offloads TCP/IP and iSCSI protocol processing from host CPU and software to silicon. The board can be used in iSCSI SAN, NAS, and standard Ethernet environments, providing a single interface for both IP storage and Ethernet/IP networking traffic.

Analysts say that an ASIC-based design is required for high performance, although a number of other I/O card vendors plan to ship "interim" cards based on software and non-ASIC RISC processors such as Intel's XScale.

Click here to enlarge image

Alacritech's board is currently available only with one port, although a dual-port version is due by the end of this quarter. "You'll really need two ports in network/SAN environments, " says Boucher, "but the advantage is still that you only need one card, as opposed to two separate cards."

Because the company is currently shipping the iSCSI TOE card to OEMs, Alacritech officials declined to provide end-user pricing, but "we expect that it will be very competitive with Fibre Channel HBAs in both price and performance," claims Boucher. However, despite the potential price parity with Fibre Channel adapters, he adds that the overall cost of iSCSI SANs will be significantly lower than Fibre Channel SANs "because you can use standard Ethernet components such as switches, and you can use the same people who build the LAN to build the SAN."

Boucher agrees with analysts who predict that smaller IT shops may experiment with iSCSI SANs in the first half of this year, but that larger IT organizations aren't likely to ramp up until at least the second half when iSCSI target devices are expected to appear. Until then, uses would have to build their IP SANs with devices (bridges, routers, or switches) or software that can covert from Fibre Channel or SCSI to IP. However, this type of configuration undermines the low cost and simplicity arguments behind IP SANs.

Debate: Full vs. partial offload

One of the major debates in the iSCSI NIC/HBA market revolves around full offload vs. partial offload of protocol stack processing. Vendors such as Alacritech use a partial offload approach, in which some of the protocol processing (mainly data control and error-handling) is handled by host software. Other vendors such as Adaptec, Emulex, and QLogic plan to implement a full offload approach, in which all protocol processing takes place in hardware on the I/O card.

This debate will not be settled until competing boards are available, enabling end users and third parties to test parameters such as overall throughput and CPU utilization. (Note: InfoStor plans to test the various boards in its lab as soon as evaluation units are available.)

null

Please enable Javascript in your browser, before you post the comment! Now Javascript is disabled.